What Is in Insulation?

When you look at a roll of insulation or a pack of batts, it can be difficult to imagine what is actually inside them. Is it glass? Plastic? Natural fibres? And how do these materials turn into something capable of keeping an Australian home cooler in summer and warmer in winter?

If you have ever wondered what is in insulation, the answer depends on the type of insulation you are looking at. There is no single material used to manufacture insulation. Instead, a wide range of natural, synthetic and mineral-based materials can be turned into insulation products, each using different manufacturing processes.

In Australia, common insulation materials include glasswool, rockwool, polyester, natural wool, cellulose, polystyrene and rigid foam products such as PIR, polyurethane and phenolic. Reflective foil insulation is another important category.

Let’s take a closer look at what is insulation made from and how some of the most common types are produced

Glasswool Insulation

Glasswool, also known as fibreglass, is one of the most widely recognised forms of insulation in Australia.

So, what is in glasswool insulation? Primarily, it is made from glass that has been heated until it melts and then spun or drawn into extremely fine fibres. Recycled glass can also form part of the raw material used to manufacture glasswool.

These fine fibres are formed into a mat and bonded together to create batts or rolls. The resulting structure contains countless tiny pockets of air. It is largely this trapped air, rather than the glass itself, that provides the insulation’s thermal resistance.

Depending on the particular product, additional materials such as binders and facings may also be present. However, the fundamental ingredient is glass fibre.

Rockwool Insulation

Rockwool, also called rock or stone wool, is another mineral-based insulation material. Rather than being made from glass, it is manufactured from mineral or rock-based raw materials.

The material is melted at very high temperatures before being spun into fine fibres. These fibres are then formed into batts, blankets, boards or loose-fill products.

Like glasswool, rockwool works partly because its fibrous structure traps large quantities of still air. It can also provide useful acoustic and fire-performance characteristics, making it suitable for a variety of Australian building applications.

Polyester Insulation

Polyester insulation is quite different from mineral wool. It is made from synthetic polyester fibres, and some Australian insulation products use recycled PET plastic as a source of those fibres. PET is the same type of plastic commonly used to manufacture products such as drink bottles.

During manufacturing, polyester fibres are formed into a flexible mat and bonded together to create batts or blankets. The finished product is lightweight and contains plenty of air pockets within its fibrous structure.

In other words, what is in insulation made from polyester? Primarily polyester fibres, with a high percentage of the fibres produced from recycled plastic.

Natural Wool Insulation

Not all insulation starts life in a factory. Natural wool insulation is made from sheep’s wool, making it one of the more obviously recognisable natural insulation materials.

The wool is processed, cleaned and formed into fibres before being manufactured into batts, blankets or loose-fill insulation. Treatments may also be applied to improve properties such as resistance to pests, moisture or deterioration. A small percentage of polyester fibres are used as a binder when forming the wool fibres into a batt or roll form

As with other fibrous insulation, the wool structure helps trap air and slow the movement of heat. However, wool also has some other amazing features – it can absorb up to thirty percent of its weight in water without feeling wet to the touch. It pulls moisture from the air when humidity rises and releases it when the air dries out, helping to regulate humidity and improve indoor air comfort.

Cellulose Insulation

Cellulose insulation is another material with a surprisingly familiar origin. It is generally made using recycled paper fibres, giving wastepaper a second life as a building material.

The paper is processed into small fibres, which can then be used as loose-fill insulation. Additional treatments such as fire retarders may be incorporated into the material to provide properties required for its intended application.

Rather than being supplied as a rigid batt, cellulose is commonly blown or installed as loose fill. The fibres create a dense layer containing many small air pockets, helping to reduce heat transfer.

Polystyrene Insulation

Polystyrene is a plastic-based insulation material that is generally manufactured as rigid boards. In Australia, both expanded polystyrene (EPS) and extruded polystyrene (XPS) are used as insulation products.

EPS is produced by expanding small polystyrene beads, which are then moulded into boards. XPS is manufactured through an extrusion process that creates a continuous foam structure.

Unlike fibrous batts, polystyrene insulation consists of a foam containing numerous small cells. These cells help limit the movement of heat through the material.

PIR and Polyurethane Insulation

Some high-performance insulation products are made from polyurethane (PUR) or polyisocyanurate (PIR). These are synthetic polymer-based materials manufactured as rigid foam boards, while polyurethane can also be used as spray foam.

Spray polyurethane foam is created by mixing chemical components that react and expand to form a foam on site.

The resulting foam contains a cellular structure that provides thermal resistance. PIR and polyurethane are particularly useful where a high level of insulation is required within a relatively limited amount of space.

Reflective Foil Insulation

Reflective insulation is different again. Instead of relying primarily on fibres or foam, reflective insulation uses a highly reflective surface, commonly aluminium foil.

Its purpose is primarily to reduce radiant heat transfer by reflecting thermal radiation rather than absorbing it in the same way as bulk insulation.

This means that when considering what is in insulation, it is important to remember that insulation doesn’t always consist of a fluffy or foamy material. A thin reflective foil can perform an insulating function too.

So, What is Insulation Made From?

As we’ve seen, there is no single answer to the question. What is insulation made from? It could be melted glass, volcanic or mineral-based materials, recycled plastic, sheep’s wool, recycled paper or synthetic polymers.

What these materials have in common is their ability to reduce heat transfer when manufactured and installed correctly. Bulk insulation generally achieves this by trapping still air within fibres, cells or other structures, while reflective insulation works primarily by reducing radiant heat transfer.

Ultimately, understanding what goes into different insulation products can make it easier to compare them. Rather than simply choosing insulation by appearance, homeowners can consider what the material is made from, how it performs and whether its properties are appropriate for their particular Australian climate and building application.